Space-Saving Antenna Solutions for Mobile Devices

Smartphones are an essential part of modern society and antennas have a vital role in the operation of the phone and mobile communications infrastructure. In recent years, smartphones with a full edge-to-edge screen and a metal rim have been the goal of the phone manufacturers but designing the antennas on such devices is demanding task. A full edge-to-edge screen significantly reduces the available room for antennas since antennas can then only be located on the rim. Compared to plastic rim, the metal rim increases the coupling, which decreases efficiency. Additionally, modern handhelds require multiple antennas to cover all of the required fifth-generation (5G) frequency bands, increase the data transfer rate, and reduce the hand effect. Implementing all necessary 5G antennas is challenging due to limited space, manufacturing cost constraints, and unavailability of decoupling structures. This thesis proposes non-conventional ways to implement antennas in limited space. First, still unused space for antenna is identified in back cover. The designed antenna achieves good performance despite the challenging position where there is only a 1-mm gap between the radiating element and the metallic battery. Noteworthily, as the back-cover antenna radiates toward the user the specific absorption rate (SAR) must be considered. This thesis proposes the following three different strategies for reducing the SAR by almost half without affecting the radiated power: specific geometry, a matching circuit, and an antenna cluster with properly calculated feeding weights. The second space-saving design is an eight-element sub-6 GHz multiple-input multiple-output antenna design that is suitable for a smartphone with a highly desirable full edge-to-edge screen and metal rim. Its compact size (17.9mm × 7mm) is achieved by bending the antenna slots. Due to three excited current modes, the frequency band is wide (3.4–6.1 GHz) and the total efficiency is high (58–95%). Additionally, manufacturing costs and even more space are saved with a simple structure that does not require any decoupling solutions. The third design proposed in this thesis saves space by integrating a sub-6 GHz antenna and a millimeter-wave (mmWave) antenna into the same volume. This shared-aperture antenna requires even less room since the sub-6 GHz and mmWave antennas have a wide frequency band (3.4–6 GHz and 26.5–29.5 GHz, respectively). Attributable to the high isolation (15.3 dB), these antennas do not interfere each other’s operation and the total efficiency is good (65–95%). Furthermore, the beam steering range of the mmWave antenna is ±}40◦. Additionally, the proposed shared-aperture antenna design is suitable for mobile devices with a full edge-to-edge screen and a metal rim. The antenna solutions developed in this thesis demonstrate how antennas can be integrated into crowded devices, where the usable space is minimal, by retaining the required technical performance while also considering the implementation aspects.